Swaging taps with uniform crest width and method of manufacture thereof

ABSTRACT

SWAGING TAPS WITH TAPERED LEAD SECTIONS SHOULD BE PROVIDED WITH THREAD CREST OF UNIFORM WIDTH THROUGHOUT THE GENERALLY CYLINDRICAL PORTION, THE LEAD PORTION AND THE TRANSITION FROM THE TAPERED PORTION TO THE GENERALLY CYLINDRICAL PORTION OF THE TAP. THE METHOD OF ACHEIVEING CRESTS OF UNIFORM WIDTH INVOLVES THE USE OF A DIFFERENT CAM TO CONTROL THE CRESTING WHEEL FROM THAT USED TO GRIND THE THREADS INITIALLY, THE WORK BEING ROTATED 180* PRELIMINARY TO ENGAGING THE CRESTING WHEEL WITH THE THREADS.

Feb. 9, 1971 J. M. N VLEET ETAL 3,561,171

SWAGING TAPS WI UNIFORM CREST WIDTH AND METHOD OF MANUFACTURE THEREOF Filed Aug; 14, 1968 2 Sheets-Sheet x In I 40 mvewrozs OHN VAN VLEET 0 Doefiaa-owskl sq i AM! 6 4* AT ORN BY,-

Feb. 9, 1971 J. M. VAN VLEET ETAL 3,561,171

' SWAGING TAPS WITH UNIFORM CREST WIDTH AND METHOD OF MANUFACTURE THEREOF Filed Aug. 14, 1968 2 Sheets-Sheet 2 Tliaus ITION SECTIONfi CYLJNDR\CAL w Poe-now 1 3v MAMA/mm ATTORNS-I$ United States Patent US. Cl. 51-288 Claims ABSTRACT OF THE DISCLOSURE Swaging taps with tapered lead sections should be provided with thread crest of uniform width throughout the generally cylindrical portion, the lead portion and the transition from the tapered portion to the generally cylindrical portion of the tap. The method of achieving crests of uniform width involves the use of a different cam to control the cresting wheel from that used to grind the threads initially, the work being rotated 180 preliminary to engaging the cresting wheel with the threads.

BACKGROUND OF INVENTION Welles Pat. 2,991,491 and Van Fleet Pat. 3,237,485 disclose taps with tapered lead sections. A single angle cam for controlling a male grinding wheel will, in every case, produce a tap in which the transition section has a double conical angle and is not on true pitch.

It will be understood that in referring to the pitch of the threads .we are referring to the thread flank intersections at the theoretical crest.

To overcome objections to lack of uniform pitch, double angle control cams were devised with a lesser angle controlling the wheel in the transition section than in the portion which controls the grinding of the rest of the lead.

Whether a single angle cam is used, resulting in threads which are out of true pitch in the transition section, or whether a double angle cam with appropriate wheel shift is used to produce threads which are precisely on pitch throughout the length of the tap, in either such case the cresting operation has heretofore resulted in deviation from uniform width in the transition zone, the crest being narrowed when the tap thread is ground with a wheel controlled by a single angle cam and widened When a double angle cam had been used to produce the top threads. These discrepancies in tap width are not of great magnitude but have been found to be very undesirable.

The present invention is based first, upon our discovery that it is desirable to maintain the crest uniform and, secondly, upon our discovery that uniformity of crest cannot be achieved in conventional practice in which the same cam is used to control the cresting wheel that was used to grind the teeth in the first instance.

SUMMARY OF INVENTION The invention produces for the first time taps having crests which are of uniform width throughout the generally cylindrical portion of the tap and the transition section thereof and the lead portion thereof. Uniform crest width has particular significance and importance in swaging taps.

According to this invention the cam used for cresting has to have a profile corresponding with the flank intersection previously ground, everything else remaining un changed.

Giving consideration to the fact that there are two basic types of swaging taps, one having a double angle cone and the other having a single angle cone in transi tion between the cylindrical portion and the lead portion, this invention has the apparently anomalous result that the single angle cam which produces the double angle cone in the transition section has to be replaced by a double angle cam for uniform cresting purposes. In contrast, the double angle cam required to produce teeth cresting a single angle cone in the transition section has to be replaced for uniform cresting purposes with a single angle cam.

Variations in the width of the crest cause inaccuracies and excessive resistance when the tap is used. The invention herein disclosed produces a swaging tap having a tooth of uniform height with a crest of uniform width and enhances accuracy and reduces the torque and the unit pressure on the most fragile portion of the thread form, the crest.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an entirely diagrammatic plan view of cam controlled grinding wheel apparatus for tap manufacture.

FIG. 2 is a diagrammatic fragmentary axial section through the transition section between cylindrical and lead portions of a swaging tap having teeth with crests in a single angle cone in the transition section. The dotted lines in this view and in FIG. 5 represent intervals of tap rotation.

FIG. 3 is a fragmentary detail view of a double angle cam which may be used to grind swaging tap teeth of the construction shown in FIG. 2.

FIG. 4 is a fragmentary view comparable to FIG. 3 showing a substitute cresting cam to replace the cam of FIG. 3 when it is desired to crest the tap threads ground with the cam of FIG. 3.

FIG. 5 is a view similar to FIG. 2 showing an older tap construction having teeth crest profiles in a double cone, one being formed by the tooth crests on the lead portion and one formed by the tooth crest transition section.

FIG. 6 is a view similar to FIG. 3 showing a single angle cam which will inevitably produce a double angle of crests in the lead and transition sections, as shown in FIG. 5.

FIG. 7 is a view similar to FIG. 4 showing a cam Which can be employed to replace the cam of FIG. 6 to produce a uniform crest on the tooth of the tap of FIG. 5

FIG. 8 is a fragmentary detail view in plan of a tootli crest showing the desired crest of uniform width.

FIG. 9 is a fragmentary view similar to FIG. 8 showing the crest of widened form which results if the cam of FIG. 6 is used to crest the tap of FIG. 5.

FIG. 10 is a fragmentary detail view similar to FIG. 8, showing a portion of a tooth crest narrowed by the use of cresting purposes of the same thread grinding cam shown in FIG. 3.

DETAILED DESCRIPTION The apparatus shown in FIG. 1 is entirely diagrammatic. Although it does not disclose any means for producing forming lobes, it may be assumed that the tap blank 12 has swaging threads 14 formed by the male grinding wheel 16.

The arbor 18 driven by motor 20 holds the wheel 16 at an angle with reference to the axis of the blank 12 in order to form the threads with proper pitch. The blank 12 is mounted on a slide 22 reciprocable in a way 24. The slide carries a fixed center 26 and a bearing 28 for chuck 30 which rotates the blank 12. Movement of the slide is controlled by feed screw 32 meshing with a nut 34 fixed to the slide.

As already stated, the lobe formation is being ignored because it is broadly irrelevant. For controlling the cone angle of tooth crests, the motor 20 and arbor 18 and wheel 16 are moved in and out in a way 36 subject to the bias of compression spring 38, the outward movement 3 being effected by a cam fixed to the slide 22 and engaged with a follower 42 connected by link 44 with an arm 46 on the slide.

The grinding wheel 16 is somewhat blunted at 48 so that the actual tooth root 50 is not at the level of the theoretical apex 52 between inwardly converging flanks.

The crest of successive turns of the thread as ground are relatively sharp as shown at 60. The apex at represents a theoretical crest at the intersection of lines extending the respective flanks. Since the opposite flanks 62 and 64 of any given turn are not ground concurrently but are ground at different times to produce crest 60, the crest may have irregularities. For this and other reasons, it is conventional to crest the thread by grinding it to a surface 66 which is axially flat. At a uniform spacing below the theoretical crest 60, the desired crest is indicated in dotted lines in FIG. 2 and is shown at 66 in FIG. 8. However, as explained in the following discussion of prior art cresting procedures, conventional cresting procedures have resulted in the transition zone 65 in a crest widened and reduced in height as shown in FIG. 9 at 66 or narrowed and increased in height as shown at 66" in FIG. 10.

Prior art cresting procedures are as follows, referring first to the tap thread shown in FIG. 2:

The grinding wheel is first re-faced as shown in broken lines in FIG. 2 to provide a broad cylindrical surface at 68. The partially completed tap is then reoriented with reference to the wheel by rotating it 180 so that the grinding wheel which originally registered with the groove or valley between the teeth in successive turns will now register with the tooth crests. Then, using the same cam 40 which was used to control the grinding wheel during the forming of the teeth, the sharp crests 60 of successive turns of the reoriented tap teeth are exposed to the surface 68 of the wheel 16. However, the profile of the crests of the teeth differs in the transition zone 65 from the path of the wheel if the wheel is being controlled by the cam 40 which formed the teeth. Consequently, use of the thread-grinding cam 40 in the cresting operation causes the wheel to produce a double angle profile. This results in an unduly deep penetration into the thread crest adjacent the angle 56 in the transition zone, and it results in the broadened crest 66 shown in FIG, 9.

In the older form of tap in which the thread is made by a grinding wheel controlled by the single angle threadgrinding cam 400 of FIG. 6, the resulting tap blank 800 of FIG. 5 has a double cone lead section, there being angles at and 92, respectively, in the transition section 65 between the tooth crest profiles in the finishing portion 94 and the tooth crest profiles in the conical lead section 96.

If it be attempted to crest the teeth of the blank 800 (FIG. 5) by using the tooth-grinding control earn 400 in accordance with conventional procedures above described, the result will be to produce in the transition section 65 as shown in FIG. 10 a tooth which will be too high above its root and will have a crest 66 which will be unduly narrow.

This invention differs from the described prior art creating practice as follows:

In addition to the above described conventional steps of cylindrically flattening the grinding wheel at 68 and relatively rotating the work 180, the present invention contemplates replacement of thread-grinding cam by a cresting cam of an angle differing from that of the toothgrinding cam and corresponding to the actual crest profile axially of the tap. Since a double-angle cam such as that shown at 40 in FIG. 3 will produce threads in the tap lead section cresting in a single conical angle, we use for cresting such a tap a cam 82 having a single angle 88 as shown in FIG. 4. The cam margin 84 is usually, but not necessarily, rectilinear and regulates the position of the cresting wheel in the generally cylindrical section of the tap. The cam margin 86 may be either curved or ree- 4 tilinear. It regulates the position of the cresting wheel in the lead section of the tap, there being a single obtuse angle 88 between the margins 84 and 86.

The profile of this cam accurately represents not only the profile of the thread as originally ground but also the profile of the desired crested tap thread. Therefore, the wheel will penetrate each successive turn only sufficiently to form a thread of uniform height and with a crest 66 of uniform width as shown in FIG. 8.

However, since the tooth crests of the tap blank shown in FIG. 5 have a double angle profile, the procedure contemplated by the present invention is to use for cresting purposes a substitute cresting cam in lieu of the toothgrinding cam 400. The cam 100 has a transition surface 102 bounded by angles 104 and 106 intervening between the edge 108 (which represents the desired tooth profile on the generally cylindrical surface of the blank) and the edge 110 (which will now regulate the cresting of the tooth in the lead section 96). Because the profile of this cresting cam matches the crest profile of the tooth crests of the double cone in the transition zone 65 of the lead section of the tap shown in FIG. 5, the resulting teeth will be of uniform height and they will have crests of uniform width as shown at 66 in FIG. 8 instead of having the defect shown at 66" in FIG. 10.

Thus, whereas past techniques have used for cresting the same cam and the same wheel used in grinding the tooth, the present invention recognizes that the profile involved in the cresting operation is different from the profile formed in the tooth-grinding operation and hence requires a different cam which must, in all instances, conform to the tooth crest profile which has resulted from the initial grinding operation. Thus stated, there is no anomaly and the tooth height will be uniform and the crests will be of uniform width in all parts of the tap.

We claim:

1. A method of making a swaging tap having a generally cylindrical portion and a tapered lead portion and a transition section between said portions and having teeth extending on at least approximately constant pitch about said portions and section and being of substantially uniform height above their respective roots and having crests of substantially uniform width, such method comprising the steps of rotating a tap blank, cam-controlled grinding of a tap thread on the blank by relative movement of a grinding wheel axially of the blank, and varying the mean position of the grinding wheel with respect to the blank in a direction which is radial respecting the tap blank, such variation occuring in the course of grinding wheel movement axially of the blank to produce said tapered lead portion, while maintaining the wheel at substantially constant radius relative to the tap blank axis to produce said generally cylindrical portion onto which said thread extends, indexing the tap approximately with reference to the wheel to register the periphery of the wheel with the crest of the thread so ground, and rotating the blank while relatively moving the tap and wheel axially of the blank along said crest while holding the wheel at a substantially constant radial distance below the theoretical intersection of the projected flanks.

2. A method according to claim 1 in which the threadgrinding step includes control of the wheel by a cam having a single angle between cam portions for controlling the relative position of the wheel in grinding the thread on the cylindrical section and on the tapered lead section respectively, thereby producing a tap having a tapered transition section of said thread between the said cylindrical section and the first said tapered lead section, and controlling the wheel in the cresting of the said thread by means of a cam different from said single angle cam and having a transition portion angularly related to the portion which controls the cresting of the thread on the cylindrical section and also angularly related to the portion which controls the Wheel in the cresting of the thread in the first mentioned tapered lead section of the tap.

3. A method according to claim 1 in which the initial grinding of the tap includes control of the relative positions of the grinding wheel and the tap blank by means of a cam having a generally rectilinear portion for controlling the production of a thread on the cylindrical portion of the blank, said cam having another portion for controlling the relative position of the wheel and the tap in the grinding of the thread on the tapered lead portion of the blank, and a well-defined third portion intervening between the first and second portions and angularly re lated to each thereof, said third portion controlling the position of the wheel with respect to the tap in the transiiton section in which the thread extends from the tapered lead portion onto the cylindrical portion of the tap, the cresting operation thereupon including the control of the relative position of the wheel and tap by a cam different from that previously mentioned in this claim and which has a single angle intervening between the portion which controls the cresting of the thread on the lead portion of the tap and the portion which controls the cresting of the thread on the cylindrical portion of the tap.

4. In a method of tap manufacture which includes the step of grinding a thread on a tap blank with a camcontrolled grinding wheel, and the step of controlling the relative position of the wheel and a tap blank including radial movement of the wheel respecting said blank to produce a threaded conically tapered lead portion while maintaining a substantially constant relationship between the tap and the wheel to produce threads on a generally cylindrical finishing portion of said tap, the improvement which consists in controlling the cresting of the thread of said tap by controlling relative positions of the tap and the grinding wheel by a cam which has a profile corresponding to the axial profile across the crests of threads produced on said portions in the thread-grinding operat1on.

5. A method according to claim 4 in which the threadgrinding step includes progressive axial offset of the grinding wheel with respect to the blank at a rate to develop swaging tap threads which are at least approximately on pitch throughout the conically tapered lead portion and generally cylindrical finishing portion of the tap, the step of radial movement of the grinding wheel respecting the blank being controlled by a cam of one profile and the step of cresting the thread of the tap being controlled by a cam having a profile differing from that of the cam which controls radial movement in developing the threads.

References Cited UNITED STATES PATENTS 1,958,105 5/1934 Koehlcr 5l288 2,991,491 7/1961 Welles 10-l52 3,023,546 3/1962 Beck 5 l288 3,226,743 1/1966 Watkins 10-152 3,323,260 6/1967 Oxford 5l288 3,237,485 3/1966 Van Vleet 76101 3,347,114 10/1967 Van Vleet 76l0l CHARLES W. LANHAM, Primary Examiner E. M. COMBS, Assistant Examiner US. Cl. X.R. 10 141, 14g 

